


Locked In

by Awkward_Ark



Category: Undertale (Video Game)
Genre: Alternate Universe - Horrortale (Undertale), Animalistic, Animalistic Sans (Undertale), Biting, Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Excessive Drool, F/M, Gen, Gender-Neutral Pronouns, Growling, Horrortale Papyrus (Undertale), Horrortale Sans (Undertale), Knotting, Locked In, M/M, Oneshot, Oral Sex, Reader Is Not Chara (Undertale), Reader Is Not Frisk (Undertale), Rough Sex, Sensitive bones, Sex, Soul Sex, also lots of purring, anal or vaginal depending on your preferance, excessive cum, heat - Freeform, lots of gowling, penatration, slight Breeding Kink
Language: English
Status: Completed
Published: 2019-07-18
Updated: 2019-07-18
Packaged: 2020-07-08 05:17:29
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,919
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19864129
Author URL: https://archiveofourown.org/users/Awkward_Ark/pseuds/Awkward_Ark
Summary: Sans' heat had come up and you were more then willing to help. The only problem was that he was feral during heats and in order to help him you would have to spend the entire week trapped in the bunker with him. And as Sans' had told you many times before, you're too determined for you're own good.Gender Neutral for everyone's enjoyment!





	Locked In

**Author's Note:**

> A big thank you to every one who follows my [Undertale Imagines](https://skelly-survival-guide.tumblr.com/) blog! I made this as gender neutral as I possibly could and I don't think it came out to bad for my first legitimate lemon. I've Rp'ed lemons before and read plenty but never written my own so this was a fun first! I hope you guys like it! Also if your a girl or imagining a girl there is a very high chance that they are leaving that bunker pregnant! XD  
> I hope you all enjoy the Sin!

You followed Papyrus down the worn concrete steps to the basement his towering form ducking to get under the old doorframe before straightening up as much as he could when he got to the other side. He was fiddling with his long fingers, obviously very nervous but trying not to fuss.

“Are You Sure You Want To Do This? He’s Very Close To Going Feral… He May Hurt You.”

His worry was touching and you honestly couldn’t ask for a better brother. He was always looking out for everyone’s wellbeing. With a small step forward you gently take his large hands into your own, rubbing you’re thumbs over his glove covered metacarpals.

“It’ll be okay Pap. I promise. Me and Sans did a lot of talking about this. I know what I’m getting into.”

“I’m Surprised He didn’t Try To Talk You Out Of It.”

You laugh a bit, head tilted down to hide your blush.

“He did at first. Turns out I’m too determined for my own good. At least that’s how he put it.”

He gave a low sigh but finally relented.

“Very Well. I’ve Said My Piece. I’ll Bring You Healing Snacks Along With The Food, Just In Case.”

A wide smile practically split your face as you wrapped your arms around his spindly waist in a tight hug.

“Thanks Pappy. You’re the best brother ever.”

His face flushed a deep rust color before he gave a happy sigh and wrapped you in a careful hug in return. After a moment he released you and started to head deeper into the basement. You had been down here a few times, looking for Sans, and had found him staring at old pieces of broken machinery that he had brought up from the Underground. He had said that he didn’t remember why he had them, just that they were important to him.

As you trailed behind Papyrus you found yourself heading deeper into the dark concrete room then you ever had before. It was mostly barren aside from a few boxes here and there and then a metal door. That was the bunker door, you realized. There was a faint shimmer of magic on the metal.

“I Suppose You Know About The Artificial Barrier Then. It’s The Only Thing Keeping Him From Taking One Of His Shortcuts Out Of The Room. Once You Go In There Is No Coming Out Until His Heat Is Over And I Can Safely Drop The Barrier. Technically You Could Destroy It With Your Human Soul However I would Only Recommend Doing That In Cases Of Emergency. You Could Do Unnecessary Damage To Yourself.”

“Don’t worry. I won’t mess with it unless it’s absolutely necessary.”

He gives a slow nod but steps aside after sliding back a latch.

“Be Careful.”

With one last smile in his direction you approach the metal door. You were a bit nervous despite the fact that you knew you wanted to do this. It would help Sans recover from his heat faster and he wouldn’t have to suffer during it. Papyrus was right, you could get hurt but you trusted Sans. You trusted him and Paps more than anyone and you knew that neither of them would deliberately hurt you. With a heavy push the door opened and you took a step through the strange almost gelatinous feeling of the tiny barrier.

The moment you stepped in his eyelight was locked on you, it was dim and seemed to be fuzzy around the edges. Ever so carefully you slid the door closed behind you and after a second you could hear Papyrus close the latch. Sans was hunched on the other side of the room in a pair of worn out basketball shorts. The tattered remains of an old white tee shirt lay scattered amongst the blankets. His signature blue hoodie had been left upstairs where it would be safe from destruction. Said destruction came from the changes to his spinous process. They had elongated and sharpened, forming a line of hard bony spines along his back.

He had told you about that as well. It was a kind of defense mechanism him and his brother started to display at some point during the famine. He also complained about not being able to lay on his back when in heat and grumbled about how itchy they could get. You were probably going to wind up scratching them for him several times while you were in here. The sudden grinding sound of his purr was what pulled your mind from its observation as he took a slow step towards you. You held your ground. He had warned you not to run and you were taking his instructions very seriously.

After a small pause he took another, then another after that. His approach was slow and calculating, as if he was trying not to scare you off. Sans had told you that backing away or trying to evade him might make him more aggressive and that was the last thing he had wanted. He was already aggressive enough when he was in heat there was no need to make it worse.

With a few more steps he had crossed the room and stood an arms distance from you, the deep bass of his purr almost made the air feel like it was vibrating around you. His clawed phalanges were twitching ever so slightly as he raised them towards you, and taking the initiative you stepped forward and pressed your cheek into the scared bones of his palm.

His purr hitched for a moment and a small bead of doubt bubbled up. What if you had done something wrong? The doubt was shattered however when his purring started up again, louder than before and with a faint rattle to his bones. The next few seconds were a blur though. There was a distinct increase in pressure, not only from his hands but the world around you as your back suddenly made contact with the wall. At some point between the dizzy spell of moving so fast and the dull ache in your spine Sans had pressed the bulk of his frame against yours. His face was buried in your hair and he was taking in deep breaths, the harsh sound of his purr still going strong.

The hand that had been cradling your head had slid down to your shoulder, kneading and pawing at it until his fingers curled and hooked into the fabric of your shirt. This was something you were expecting so you had taken the liberty of wearing clothes that you didn’t care about and not wasting time on underwear. And on que he started to rip, the fabric pulling taunt over your skin before tearing under the pressure. He had only freed one arm though until his other hand came up on your other side and started to rip and pull there as well.

He would have to back up to get the shirt off in one go but he didn’t seem to want to, only pressing his ribs more firmly against your chest as if it would relieve a deep ache. As his hand continued to slowly rip away at the fabric you raised your hands in return, gently placing them against his ribcage. His movements halted for just a second as he shuddered and you took it as a good sign. Hands slowly sliding along the scared surface until your fingers just ghosted over one of his vertebrae. His purr warped into a low snarl as his hands stilled to grip you sides and he ground his pelvis against you. There was a prominent bulge already, a dim blue glow coming from his shorts.

You left one hand there, ever so carefully leaving feather soft caresses to his spine while the other drifted a bit lower to his floating ribs, hooking your fingers just beneath them and pulling forward. The grip he had on you was likely to leave bruises as he shuddered and rattled, his voice not being able to make up its mind on whether he was supposed to be growling or purring. The sounds hitching from one to the other as he rocked himself against you.

He was lost in the haze of his heat and while it was intimidating, how open he was right now was endearing in its own way. Cautiously you turned your head and gently pressed your lips to the bottom of his mandible, leaving a line of soft, slow kisses as you continued to trace his bones.

His arms clamped around you as he pulled you both away from the wall. The sudden movement had you gripping to his ribs as he carried you over to the pile of blankets in the corner. He didn’t give any warning or loosen his grip as he dropped to his knees and started to lean forward. Even now, in his makeshift nest, he still kept you pinned with his ribs. But now when you glanced to his face he was looking around, fuzzy red eyelight dilated to the size of a small coin. He was stock still, scoping out the room for any apparent danger as his growl lowered in pitch.

Whilst he was distracted by his paranoia you managed to pull off the remaining rags of your top, sighing as your bare chest pressed into his heated bones. The soft press of your skin must have caught his attention though because the red glow of his eye was back on you, or more specifically, it was trained on your now exposed chest. He sat up, despite your protesting hands trying to pull him back down, and stared down at you. His hands running over and groping at any soft flesh they could reach. The rough scrape of his clawed digits making a small moan filter from your mouth. You still tried to pull him back down though, it was chilly down here and he was warm. There were goosebumps forming on your arms and your nipples had definitely hardened, which only made his touch that much more intense, the flash of heat over chilled flesh.

His eyelight dragged down lower, his hands sliding down right behind it, until he got to your pants. They were nothing more than an old pair of workout pants but he seemed offended that they were still on as he quickly ripped them straight down the middle. And as you had elected to skip underwear this left your most vulnerable region bare to the cold air and his hungry gaze.

You couldn’t hold back the small squeak that left you when he grabbed your thighs and yanked them upward till you were nearly upside down, forcing you to release his ribs in the process. This time it was your turn to jump and shudder as he drags his tongue over your nethers, leaving behind an unusually slimy line of tingling, magic drool in his wake. It was a whole lot more drool then he normally produced and you had a feeling you knew why.

A gasp tore from your lips as said tongue started to prod at your entrance, slathering it in more viscous drool and slowly pushing its way in. The feeling of his tongue pressing and rubbing against your inner walls sent a spark up your spine as you gripped at his fingers. This wouldn’t last long and you knew it but it didn’t stop the moans that poured from your lips or the way you tried to rock your hips against his face.

And you were right it didn’t last long. After just a few moments he pulled back, his tongue sliding out of you with a wet squelching sound, a testament to how much drool he had been producing. That and the drool still dripping down his jaw when he dropped you back down onto the blankets. As you lay there you got a brief moment to really look at him, this close you could see the glow of magic build up between his joints, it was both eerie and beautiful at the same time. In That moment you took to observe him however he had ripped away at his own shorts and pulled you from your thoughts by grabbing your thighs again. He was pressing them forward, up towards your chest until you couldn’t bend anymore.

He was purring down at you again, a few drops of drool dripping down and landing on your chest. You could feel his member rubbing against you, almost desperately, and then he leaned down replacing his hands with the weight of his shoulders and chest to keep you bent and pinned. One of his now free hands was groping at your thigh while the other went lower and he lined himself up.

The head of his dick prodded and rubbed for just a moment before with one harsh push, he pierced his way in. His girth was a bit thicker than usual, making you wince at the stretch but he didn’t really give you much time to adjust as he shifted his hips to push in as far as he could until he had sheathed himself entirely inside of you. A small whine left you as he began to rock, he was definitely bigger than normal and you could feel every ridge on his cock catching and pulling on your inner walls.

With every pump he made he got a bit rougher. Pulling out farther and thrusting back in with increased force. His growled moans above you were just as intoxicating as his touch. You were trying to touch him as well but with your position you had a very limited reach and had to settle for rubbing and scratching along the sides of his ribs.

In the midst of his rough attentions however you missed his hand coming up until it was tangled in your hair and yanking your head to the side. The sharp pain drew a small cry from you and a harsher thrust from him as you clenched around him. Your growly mate’s eye was locked on the bite scar that stretched over your shoulder, his mark. And with his next thrust his head darted down, jagged teeth latching into your shoulder once again. Your breathing hitching as you felt your skin give way under the sharp pressure. It hurt but not nearly as badly as the first time he did it.

Once he had your shoulder in his maw his pace picked up again. He was getting bigger, you could feel it. His member was getting caught on your entrance as he continued his forceful pumps and his growls were increasing in volume. A small part of you was panicking that it wouldn’t fit if it got any bigger but the majority of your mind was lost in a haze of your slowly building orgasm.

You felt the pinch when he pulled your soul free, the dim glow of its light coloring the small gap between your chests as everything else went dim. It was quickly followed by the soft white glow of his own soul. You couldn’t look away as the two souls danced around one another, distracting you from the nearly painful way his swelling member was catching with every thrust. Until his soul cornered yours and pressed into it. Then you could feel it all with such an intensity that you couldn’t even think. The sharp pain of his still clamped jaw, the sting you felt with every new thrust and the pure animalistic pleasure coursing through his bones. It was the most wonderful thing you had ever felt, nothing but unbridled bliss as you clamped down in the most powerful orgasm you had ever experienced.

As your pinned body writhed beneath him he gave one final snarl and forced his knot back in one last time, holding you still as he finished swelling and started to release his magic into you. You didn’t even get the chance to come down from your orgasm as the sparking magic started to flood you, only adding to the intense pressure that was already there and sending you right back over the edge you had just gotten off of. You couldn’t take anymore as your eyes rolled back and your body went limp beneath him.

When the haze left your mind he was still above you, but had let your legs fall to the side and his tongue was lapping softly at your throat with a deep purr. You were still tied together, the pressure was unmistakable, especially when he twitched and released yet another wave of magic into you.

You knew you’d be beyond sore at the end of this week, hell you didn’t think you’d be able to walk for a month if it continued like this but it was worth it. A soft smile tugged at your lips as you gently rubbed at his neck then let your fingers slide to his sharpened spinous process and ever so carefully scratched at them. You had been expecting him to lean into it or attempt to shake your hand away. What you hadn’t been expecting was for his purr to kick up a notch and for him to collapse on top of you. You huffed and wheezed at the sudden weight but he just shifted his spines back into your hand, the purring bastard turning to lick at your cheek. This really would be a long week.


End file.
